quaybackstop: add backstop GC command

This command should allow a Clair+Quay system to periodically ensure
that the Clair database is not continuing to store manifests that no
longer exist in the Quay database.

Signed-off-by: Hank Donnay <hdonnay@redhat.com>

.dockerignore

@@ -11,6 +11,7 @@ NOTICE
 # Directories
 /book
 /contrib
+!/contrib/cmd
 /Documenatation
 /etc
 /local-dev

contrib/cmd/quaybackstop/Dockerfile

@@ -0,0 +1,56 @@
+# syntax=docker.io/docker/dockerfile:1.7
+
+# Copyright 2024 clair authors
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+# This Dockerfile expects the context to be the root of the repo, e.g.:
+#     go run github.com/moby/buildkit/cmd/buildctl@latest build \
+#     --frontend dockerfile.v0 \
+#     --local context=. --local dockerfile=contrib/cmd/quaybackstop
+
+ARG GOTOOLCHAIN=local
+ARG GO_VERSION=1.23
+FROM --platform=$BUILDPLATFORM quay.io/projectquay/golang:${GO_VERSION} AS build
+WORKDIR /build
+RUN --mount=type=cache,target=/root/.cache/go-build \
+	--mount=type=cache,target=/go/pkg/mod \
+	--mount=type=bind,source=go.mod,target=go.mod \
+	--mount=type=bind,source=go.sum,target=go.sum \
+	go mod download
+
+ARG TARGETOS
+ARG TARGETARCH
+ARG TARGETVARIANT
+RUN --mount=type=bind,target=. \
+	--mount=type=cache,target=/root/.cache/go-build \
+	--mount=type=cache,target=/go/pkg/mod \
+	--network=none \
+	<<.
+set -e
+export GOOS="$TARGETOS" GOARCH="$TARGETARCH" GOBIN=/out/bin CGO_ENABLED=0
+if [ -n "$TARGETVARIANT" ]; then
+	case "$TARGETARCH" in
+	amd64)  export GOAMD64="$TARGETVARIANT" ;;
+	ppc64*) export GOPPC64="$TARGETVARIANT" ;;
+	esac
+fi
+install -d "${GOBIN}"
+go build -ldflags="-s -w" -trimpath -o "${GOBIN}" ./contrib/cmd/quaybackstop
+.
+
+FROM gcr.io/distroless/static:nonroot AS final
+COPY --from=build /out/bin/quaybackstop /
+WORKDIR /run
+USER 65532:65532
+ENTRYPOINT ["/quaybackstop"]